You may try a photoresist reflow technique.
First pattern photoresist and reflow in a heated oven
This technique has been used to make microlense.

Jaephil Do, Graduate Research Assistant
Microsystems and BioMEMS Lab. Rhodes hall #919
Dept. of ECECS, University of Cincinnati
Cincinnati, OH 45221-0030
Phone: (513) 556-0852, Fax: (513) 556-7326
eMail: dohj@ececs.uc.edu

-----Original Message-----
From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org]
On Behalf Of Joseph Grogan
Sent: Monday, June 26, 2006 12:40 PM
To: General MEMS discussion
Subject: Re: [mems-talk] How to fabricate rounded channels

Ho big does your channel need to be?
-Joe Grogan

t yt wrote:
> Hi all,
>
>   I want to fabricate a rounded channel from PDMS. Still i have no idea
about how to fabricate a rounded mold. Is there anyone who can give me
suggestion?
>